1. Field of the Invention
The present invention relates to an optical disk apparatus and, more particularly, to a laser beam control apparatus for controlling a laser beam irradiated from the light source of the optical head of the control apparatus onto an optical disk.
2. Description of the Related Art
An image filing system uses an optical disk apparatus. In this optical disk apparatus, while an optical disk, on which a large number of tracks are spirally or concentrically formed, is rotated, data is recorded or reproduced on or from the tracks.
A document is two-dimensionally scanned to photoelectrically convert the image data of the document into electrical image data, and this electrical image data is optically recorded on tracks of the optical disk by means of an optical head. In the retrieval mode, this recorded data is retrieved by the optical head to be reproduced as a hard or soft copy.
In the optical disk apparatus, after data is recorded on the optical disk by a laser beam output from a semiconductor laser oscillator (light source) in the optical head, or data recorded on the optical disk is read by converting it into an electrical signal by using a detector in the optical head, and subsequently converting the electrical signal into a video signal.
The amount of the laser beam emitted from the semiconductor laser oscillator is controlled by a laser beam controller. This laser beam controller is designed to correct changes in laser beam with changes in temperature of the semiconductor oscillator by correcting a threshold current by means of feedback control using a monitor current with respect to the laser beam, thereby keeping the light amount constant.
More specifically, a monitor current with respect to a laser beam from the semiconductor laser oscillator is output from a photodiode. The output monitor current is then converted into a voltage. The amount of the laser beam emitted from the semiconductor laser oscillator is controlled in accordance with this voltage.
In such a conventional apparatus, however, since the band of this control is narrow, the laser beam output power of the semiconductor laser oscillator varies due to return light noise. This inevitably influences data and control signals. In addition, due to an insufficient response speed with respect to a recording pulse, light amount control based on a feedback control scheme cannot be performed.